build: musl static by default, glibc optional, strip the release binary

configure.ac

@@ -2,9 +2,38 @@ AC_PREREQ([2.69])
 AC_INIT([fastwc], [0.1.0], [], [fastwc])
 AC_CONFIG_SRCDIR([src/main.c])
 
+# Build flavor: --enable-glibc links dynamically against the system libc
+# (respecting CC, whatever it is). The default is a fully static musl
+# binary, preferring musl-gcc even when CC is set in the environment,
+# since removing ld.so from startup is exactly what the tiny-file
+# benchmark races hinge on.
+AC_ARG_ENABLE([glibc],
+  [AS_HELP_STRING([--enable-glibc],
+    [link dynamically against the system libc (respects CC) instead of the default static musl])],
+  [enable_glibc=$enableval], [enable_glibc=no])
+
+STATIC_LDFLAGS=
+if test "x$enable_glibc" = xno; then
+  # Static musl is the default toolchain. Fall back to the system
+  # compiler (dynamic link) only when no musl compiler is installed.
+  AC_PATH_PROGS([MUSL_CC], [musl-gcc x86_64-linux-musl-gcc])
+  if test -n "$MUSL_CC"; then
+    CC="$MUSL_CC"
+    STATIC_LDFLAGS="-static"
+  fi
+fi
+
 AC_PROG_CC
+AC_CHECK_TOOL([STRIP], [strip], [:])
 AC_USE_SYSTEM_EXTENSIONS
 AM_INIT_AUTOMAKE([foreign subdir-objects])
 
+AS_IF([test "x$enable_glibc" = xyes],
+  [AC_MSG_NOTICE([fastwc: glibc build requested, using $CC])],
+  [AS_IF([test -n "$MUSL_CC"],
+     [AC_MSG_NOTICE([fastwc: building against static musl ($MUSL_CC)])],
+     [AC_MSG_WARN([fastwc: musl-gcc not found; falling back to $CC (dynamic link). Install a musl toolchain or configure --enable-glibc.])])])
+AC_SUBST([STATIC_LDFLAGS])
+
 AC_CONFIG_FILES([Makefile])
 AC_OUTPUT